051 Isovolumetric Contraction

Isovolumetric contraction is that stage when the ventricles continue to contract even though the blood volume stays the same. How and when exactly do this happen?

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Transcript of Today’s Episode

Hello and welcome to another episode of Interactive-Biology TV where we’re making Biology fun. My name is Leslie Samuel and in this episode, Episode 51, I am going to talk about isovolumetric contraction. So, let’s get right into it.

What we’re looking at here is diastole at the top and systole at the bottom. So, this is where the ventricles are relaxing and this is where the ventricles are contracting. As you can see, blood is flowing into the atria and then, into the ventricles. Then, when the ventricle contracts, that pushes the blood into the aorta so that, it can go to the rest of the body and also, send blood to the lungs.

There’s something very significant that’s happening here. When the blood comes in, you can see this atrioventricular valve is open to let that blood get in to the ventricle. Once the ventricles contract, that causes this atrioventricular valve to close and of course, the same thing over here, so that the blood does not flow back into the atria.

We see here that this semilunar valve is open. However, that does not happen immediately. When the ventricle contracts, it needs to build up enough pressure to open that valve so that, the blood can flow out of the ventricle and to the rest of the body.

What we’re going to look at over here is what we’ve looked at before where right after the ventricular contraction happens, the cycle starts over and the ventricle fills with blood. So, you’re going to see an increased volume in the ventricle. And then, at a certain point, the atria are going to contract so, when the right atrium contracts, that forces even more blood faster into the ventricle. So, when the left atrium contracts, that forces more blood faster into the left ventricle and then, the ventricle contracts. When it contracts, that is going to push blood out of the ventricle and it’s going to go to the rest of the body. This is the end diastolic volume here and here we have the end systolic volume.

Let’s look at what’s happening in the ventricle when it comes to pressure. During the relaxation period, the diastole, we’re not going to have any pressure in the ventricle. So, we hardly have any so, I’m going to put that around zero. Then, at a certain point, let’s say at this point here, we have the atrium contracting, and when the atrium contracts, that’s going to cause an increase in pressure in the ventricle. Not a huge increase, but, an increase nonetheless. Then, the ventricle is going to contract. When the ventricle contracts, that’s going to cause an increase in pressure in the ventricle.

Let me draw that here. Here, we have that increase in pressure but, as you can see, it’s not until we reach this point that the valve actually opens, the semilunar valve opens, so that the blood can flow out. This is the point that we need to reach. Let’s say that that point is somewhere around 80 mL of mercury so, the pressure has to reach approximately 80. When that happens, the semilunar valves open and the blood gets ejected. We still have some increase in pressure and then, at a certain point, the muscle relaxes, we get diastole, and the pressure comes back down.

This time period, between where the ventricle contracts but the blood does not get ejected, and this point, we call this, (let me do that in a different color), we call this isovolumetric contraction. Why do we call it isovolumetric contraction? “Iso-” refers to the fact that it’s the same; “volumetric ” refers to volume so, the volume stays the same; “contraction” because the ventricle is actually contracting even though the volume is staying the same. The reason the volume is staying the same, is because the valves are closed so, the blood cannot leave until it reaches that point where the semilunar valve opens. Once that opens, the blood can flow out to the rest of the body.

That’s it! That’s the concept of isovolumetric contraction. That is all I want to cover in this episode. As usual, I’d like to invite you to visit the website at Interactive-Biology.com for more Biology videos and the many other resources we’re adding over time. Our goal is to help make Biology fun. That’s it for this video and I’ll see you on the next one.